Does It Matter When You Eat?

Science has a new answer

When you're trying to lose weight, what you eat certainly matters. But what about when you eat? As it turns out, timing might actually be a key factor in determining your success with the scale.

In a study published in the International Journal of Obesity, researchers followed 420 overweight and obese women over a 20-week span. Study participants were divided into two groups: Half of participants ate their midday meal (the largest of the day, comprising around 40% of total calories) before 3 o'clock in the afternoon, while the other half scarfed it down later on.

Those in the second group lost 25% less weight, and experienced a slower rate of weight loss, compared to individuals dining earlier in the day. Furthermore, researchers noted that participants in both groups ate a similar number of calories and expended a similar amount of energy. So even though women eating lunch later exercised as much as their peers, and ate the same amount of food, their bodies simply didn't cooperate with weight loss efforts to the same extent.

The findings don't establish a cause-and-effect relationship between meal timing and weight loss, but they do corroborate earlier animal studies. Research on mice published in Cell Metabolism, for instance, noted that mice with restricted meal times lost more weight than those who ate whenever they wanted—despite having the same caloric intake.

Experts involved in this latest study suggest that a disruption of the body's circadian rhythms might explain the connection. "With meals at strange times, you may get an uncoupling of all the clocks in the body," says study author Frank Scheer, PhD, an associate neuroscientist at Brigham and Women's Hospital in Boston. "It's like a conductor losing track of his orchestra, and everyone starts playing to their own tune." This lack of synchronicity might impact how the body metabolizes food and stores energy.

The takeaway? It's too early to make solid recommendations from the research, Scheer says, though he acknowledges that "this study reminds us to think about when we eat, not only what we eat." Of course, there are plenty of other advantages to dining earlier in the day: A ton of research has shown that a hearty breakfast boosts metabolism and curbs cravings, and that late-night eating often derails otherwise healthy diets.